1. Technical Field
The present invention relates to a dimming control device, an image display device, and a dimming control method.
2. Related Art
As an example of a display device, there has been known a projection display device (a liquid crystal projector) for projecting an image emitted from an optical system using a liquid crystal light valve on a screen in an enlarged manner with a projection lens.
However, such a projection display device has a problem that it is difficult to obtain sufficient contrast due to light leakage or stray light caused in a variety of optical elements constituting the optical system. In order to resolve such a problem, it is sufficient to, for example, vary the intensity of the light to be input to a liquid crystal light valve in accordance with an image signal. However, a high-pressure mercury lamp predominates as the light source used for the projection display device in the present circumstances, and there is a situation in which it is extremely difficult to control the light output intensity of the high-pressure mercury lamp itself.
Further, since the luminance of the light source is fixed as described above, there also arise a problem that the screen is too bright in, for example, a rather dark appreciation environment and a problem that the brightness of the screen varies in the case of changing the size of the projection image due to zooming.
Therefore, as an illumination device for the projection display device, there has been proposed a configuration provided with a dimming element having a structure of combining a louver (a light blocking plate) for dimming with respect to the light source, and performing control so that the light-blocking amount with respect to the outgoing light from the light source is varied in accordance with the image signal using the dimming element. Thus, the change of the light intensity of the light emitted from the light source can be performed at high speed and with high flexibility using the dimming element separated from the light source (see, e.g., JP-A-2005-10354).
However, in the case of performing the dimming control by the dimming element provided with the light-blocking plate as described above, the larger the dimming amount is, the more easily the color shading in the display image occurs.
In the liquid crystal projector, a fly-eye lens is disposed along a surface perpendicular to the light axis of the light emitted from the light source. The light emitted from the light source is divided by the fly-eye lens into a plurality of lights, and thus, the illuminance distribution of the light entering the liquid crystal light valve is homogenized.
By increasing the dimming amount using the dimming element provided with the light blocking plate, the number of lens cells through which the light is transmitted in the fly-eye lens decreases, which causes the color shading in the image displayed on the screen.